Complaint of elderly relative that is opposed to entering church (9)
I believe the answer is:
grievance
'complaint' is the definition.
(grievance is a kind of complaint)
'elderly relative that is opposed to entering church' is the wordplay.
'elderly relative' becomes 'gran' (I've seen this before).
'that is' becomes 'ie' ('i.e.' can be a synonym of 'that is').
'opposed to' becomes 'v' (abbreviation for versus).
'entering' is an insertion indicator.
'church' becomes 'ce' (abbreviation for Church of England).
'ie'+'v'='iev'
'gran' going around 'iev' is 'grievan'.
'grievan'+'ce'='GRIEVANCE'
'of' acts as a link.
(Other definitions for grievance that I've seen before include "gripe" , "Reason for dissatisfaction" , "Complaint" , "beef" , "Bad feeling" .)